Magnetic amplifier output signal control system



Nov. 22, 1960 R. D. PETTlT 2,961,598

MAGNETIC AMPLIFIER OUTPUT SIGNAL CONTROL SYSTEM Filed 001;. 24. 1955 l4 FIGJ. A LOAD n 24 M A 5; u 7 ll 27 2: G40 if -aa y FIG.2

LOAD

INVENTORI RICHARD D. PETTIT,

BY 77MM HIS AGENT.

United States Patent MAGNETIC AMPLIFIER OUTPUT SIGNAL CONTROL SYSTEM Richard D. Pettit, Rugby, England, assignor to The British Thomson-Houston Company Limited, a British company Filed Oct. 24, 1955, Ser. No. 542,376

6 Claims. (Cl. 32389) This invention relates to the art of electric control apparatus, and more particularly to the art of signal control of magnetic amplifier output.

In the stabilization of automatic signal control systems employing magnetic amplifiers, it is often necessary to feed back into a magnetic amplifier a current derived from a change in voltage occurring elsewhere in the system. Heretofore, such current has been fed into a control winding on the magnetic amplifier, where this control winding has been provided specifically for this purpose, or the current has been combined with other control signals and applied to an existing control winding or windings.

To secure the desired effect from the stabilization signal, it is oftentimes desired that a delay should exist in the feedback circuit, that is, a delay between the application of the change in voltage to the terminals of the circuit and the dying away of the current produced thereby in the feedback circuit. For the feedback to be effective in stabilizing some types of automatic control system, the delay is often required to have a time constant of the order of one second. This may be obtained by means of a series resistance and capacitance in the feedback circuit. The time constant is then proportional to the product of resistance and capacitance, i.e., R, C, where R includes the resistance of the control winding.

It is obvious, however, that increasing the resistance to increase the time constant will reduce the current and, therefore, the effect of the feedback. The value of R is determined by the magnitude of feedback voltage available and the current necessary in the control circuit to obtain stability. Therefore, a large value for C is required to obtain the desired time constant.

One object of the present invention is to make the time constant of a feedback circuit much greater than that determined from the values of R and C, by virtue of its connection to the amplifier.

Another object of this invention is to provide a simple feedback circuit for a magnetic amplifier which is efficient in operation.

Another object of this invention is to provide efiicient stabilization of control systems.

A further object of this invention is to provide an improved electrical signal control method and arrangement.

A feedback circuit constructed in accordance with one embodiment of the present invention will supply current derived from a change in voltage occurring in the system through the series connected circuit of a capacitor and the load current windings of a self-saturating full-wave magnetic amplifier. The feedback connection is phased so that the voltage developed in each load current winding in turn, due to the resultant change in load current flowing in the resistance of the winding, is of the polarity to reduce the rate of change in charge of the capacitor, and so to increase the effective time constant of the circuit.

In accordance with a modification of my invention, a bridge circuit is provided to give a direct current output.

The features of my invention, which I believe to be 2,961,598 Patented Nov. 22, 1960 novel, are set forth with particularity in the appended claims. My invention, itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in which:

Figure l is a schematic diagram of a magnetic amplifier circuit in accordance with an embodiment of the present invention.

Figure 2 represents an operating characteristic of a portion of a circuit shown in Figure l, and

Figure 3 illustrates a modification of the circuit shown in Figure l.

in Figure l of the drawings the magnetic amplifier circuit embodying the present invention is shown to include a source of undulating potential 19, such as an alternating voltage generator, having one of its terminals connected through a load circuit 11, such as a utilization impedance, to terminal 12 and a second terminal connected directly to terminal 13. A rectifier 14 and a load circuit winding 15 are connected in series across terminals 12 and 13. The rectifier 14 is so connected as to conduct when terminal 12 is positive with respect to terminal 13. A second rectifier 17 and a second load circuit winding 18 are connected in series across term-rials 12 and 13. The second rectifier 17 is so connected as to conduct when terminal 13 is positive with respect to terminal 12. The load circuit windings are wound on cores 19 which are adapted to saturate in response to a predetermined signal. Wfndings 20 and 21 bias the cores 19 to a desired level in accordance with the voltage applied by generator 22. As described thus far, the circuit will be recognized as a conventional doubler circuit well known to the art. Normally load current due to the source 10 will flow in windings 15 and 18 alternately as indicated by arrows A and B. The magnitude of these currents will be determined by the amplitude of the source voltage, the load impedance, and the degree of saturation in the cores provided by the direct current control winding or windings.

In many applications the feedback voltage from the controlled circuit is applied to the control windings. However, such utilization of the feedback requires excessively large capacitance to provide a time constant of the order of magnitude frequently required in such circuits. The source of feedback voltage 23, which may be a means for deriving a voltage responsive to the energy in the load circuit 11, is connected through a series capacitance 24 and resistance 25 across the windings 15 and 18 by connection at terminals 26 and 27.

The operation of the circuit in Figure 1 may best be understood by reference to Figure 2, wherein the current flowing through load 11 is plotted as the ordinate and time is plotted as the abscissa. In Figure 2 the curve above the X axis represents current A and the curve below the X axis represents the current B. If, during normal operation, a change in voltage from the controlled circuit is fed back so as to cause terminal 26 to be positive in electric potential with respect to terminal 27, a current will flow through the main load current windings of the saturable magnetic amplifier. If this voltage is applied, for example, at time T, as indicated in Figure 2, the transient current produced by the voltage in changing the charge of capacitor 24 will flow through winding 15 without any noticeable effect, since this winding is carrying the load current and the associated core 19 is saturated. However, the flow of the transient current through winding 18, which is not carrying load current, will cause the core polarization, i.e., its initial saturation, to change by an amount dependent upon the magnitude of the charging current. When winding 18 starts to carry load current on the next cycle of the voltage applied by generator 10, the core will saturate earlier in the cycle and an increased load current will result as shown by the shaded portion 30 in Figure 2. During this half cycle, the polarization of the core of winding 15 will be changed in like manner and, therefore, increased current will flow in the load circuit until capacitor 24 is charged to the new voltage and the transient has died away. It should be noted that the total core polarization is the sum of that produced by the transient charging current and that by the control winding or windings.

The increment of load current caused by the effect of the transient charging current on core polarization will develop a corresponding voltage increment across each main winding. This increment of voltage is proportional to the increment of load current times the resistance of the winding, and the polarity of the incremental voltage will be such as to oppose the current flow in the feedback circuit resulting from the transient voltage. Since the coil winding is so adjusted that the incremental voltage across each load current coil opposes the voltage supplied by the circuit represented by the generator 23, the rate of change of charge upon capacitor 24 will be decreased, thus effectively increasing the time constant of the feedback circuit.

In certain instances, resistor 25 may be eliminated by proper design if desired. However, it is usually convenient to substitute a variable resistance to obtain a simple method of adjusting the effective circuit time constant.

It will be obvious to those skilled in the art that the circuit will be effective if the polarity of the source of feedback voltage is such as to make terminal 27 positive with respect to terminal 26. The load current in each winding will, in this case, be reduced, thus the polarity of the incremental voltages developed will continue to oppose the change in charging current of the capacitor with the desired result of effectively increasing the time constant of the feedback circuit.

It will be obvious to those skilled in the art that a magnetic amplifier having feedback applied thereto in accordance with this invention, may have additional positive or negative current feedback from the load circuit and external control devices applied to the existing control winding. A representative feedback control system is shown in Figure 1, where generator 22 represents the combined feedback from the load, as well as external control voltage or either signal alone. Such modifications are obvious to those skilled in the art and come within the scope of this invention.

The circuit shown in Figure 1 can be modified to produce direct current in the load. One embodiment of such a modification is shown in Figure 3, in which components identical with those of Figure l are identically numbered. In this embodiment, the source It) has one terminal connected directly to terminal 12. Rectifiers 31 and 32 are connected in bucking relationship with rectifiers 14 and 17, respectively, forming a bridge circuit. The load 11 is connected across the arms of the bridge at terminals 33 and 34. The saturable cores of the load circuit windings 15 and 13 are not shown.

The circuit operates in a manner similar to that of Figure 1, except that the rectifier bridge connection provides direct current output through the load.

While particular embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modifications'as fall within the true spirit and scope of the invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A magnetic amplifier of the full-wave self-saturating type having two saturable core members, each of said core members including a load current winding wound thereon, a load circuit comprising a first and second input terminal, a third terminal, two unidirectionally conducting devices, means for connecting each of said unidirectionaily conducting devices in a different polarity through a respective winding between said second and third terminals, a first source of alternating electrical signals coupled between said first and third terminals, a second source of signals, means for causing a change in the signal of said second source. to produce a transient deviation in the signals supplied to said load circuit by said first source such that the period of transient deviation is extended beyond the duration of the signal change of said second source, comprising means for coupling said windings to said second source.

2. A magnetic amplifier of the full-wave, self saturating type having two saturable core members, each of said core members including a load current winding wound thereon, a load circuit comprising a first and second input terminal, a third terminal, two unidirectionally conducting devices, means for connecting each of said unidirectionally conducting devices in a different polarity through a respective winding between said second and third terminals, a first source of a'ternating electrical signals coupled between said first and third terminals, a second source of signals, means for causing a change in the signal of said second source to produce a transient deviation in the signals supplied to said load circuit by said first source such that the period of transient deviation is extended beyond the duration of the signal change of said second source, comprising means for coupling said windings to said second source, said last named means comprising means for coupling a capacitance and said second source in series between the junction each of said unidirectionally conducting devices with its respective winding.

3. A magnetic amplifier as claimed in claim 1 having a control winding wound on each of said saturable core members, and means for energising said control windings to further control the current flow in said load circuit.

4. A magnetic amplifier of the full-wave, self-saturating type having a first saturable core member, including a load current winding wound thereon, a first unidirectionaly conducting device connected in series with said winding, 2. second saturable core member, including a second load current winding wound thereon, a second unidirectionally conducting device connected in series with said second winding, a load circuit, an alternating voltage source for supplying electric energy to said load circuit and current windings, said source having a first and second terminal, means connecting said first terminal to said load circuit, means connecting said series connections of devices and windings between said load circuit and said second terminals, said first unidirectionally conducting device adapted to conduct when said first terminal is positive with respect to said second terminal, said second unidirectionally conducting device adapted to conduct when said second terminal is positive with respect to said first terminal, means for deriving a direct voltage responsive to the energy said load circuit, said means having a positive and negative terminal, means connecting said positive terminal to said first load current winding, at the junction between saidwinding and said first unidirectionally conducting device, said connecting means comprising resistance and capacitance, means connecting said negative terminal to said second winding at the junction between said winding and said second unidirectionally conducting device.

5. A magnetic amplifier as set forth in claim 4 in which said first and second saturable cores have a respective first and second control winding wound thereon, and means for energizing said control windings to further control the current flow in said load.

6. A magnetic amplifier output signal system for controlling the variation in electric power delivered to a load circuit comprising a load circuit, a magnetic amplifier of the self-saturating type arranged to deliver electric power to said load circuit, means for deriving a sig- References Cited in the file of this patent UNITED STATES PATENTS 2,561,329 Ahlen July 24, 1951 Silver et al. Oct. 18, 1955 Clark Dec. 25, 1956 Schmidt Sept. 24, 1957 Ecizert Apr. 8, 1958 OTHER REFERENCES Publication: Flux Preset High-Speed Magnetic Arnplifiers, by C. B. House; A.I.E.E. Transactions, vol. 72, part I, 1953, pages 728-735. 

